Taking aspirin daily is not a quick or reliable way to prevent bowel cancer for most people, according to a new Cochrane review. This analysis also highlights some clear downsides. Regular use of aspirin increases the risk of serious bleeding soon.
Bowel cancer, also known as colorectal cancer, is one of the most common cancers worldwide. Prevention usually focuses on healthy lifestyle choices and regular screening tests. In recent years, scientists have investigated whether widely available drugs such as nonsteroidal anti-inflammatory drugs (NSAIDs) may help lower the risk.
NSAIDs, such as ibuprofen and aspirin, are commonly used to treat pain, inflammation, and fever. However, whether these drugs can prevent colorectal cancer before it occurs remains unclear and widely debated.
To better understand the evidence, researchers from West China Hospital of Sichuan University in China reviewed 10 randomized controlled trials involving 124,837 participants. They investigated whether aspirin or other NSAIDs could reduce the risk of colorectal cancer or precancerous growths (adenomas) in people with average risk. No eligible trials were found for non-aspirin NSAIDs, so this result applies only to aspirin.
Limited short-term effects and uncertain long-term effects
The review found that aspirin is unlikely to reduce the risk of colorectal cancer during the first 5 to 15 years of use. Some studies suggest that there may be a protective effect after more than 10 to 15 years of follow-up, but confidence in this evidence is very low.
These long-term benefits may result from an observation period after the initial trial ends. During that time, participants may stop taking aspirin, start using it on their own, or start other treatments. These factors make the results susceptible to bias.
Lead author Dr. Zhaolun Cai explains: “While the idea that aspirin protects against colorectal cancer in the long term is intriguing, our analysis shows that this benefit is not guaranteed and carries immediate risks.”
The risk of bleeding with aspirin begins immediately
Researchers also found strong evidence that daily aspirin intake increases the risk of serious extracranial hemorrhage and is likely to increase the risk of hemorrhagic stroke.
Higher doses are more dangerous, but even low doses (“baby”) of aspirin increase the chance of bleeding. Older adults and people with a history of ulcers or bleeding disorders may face particularly high risk.
For this reason, the authors emphasize that potential long-term cancer benefits must be carefully weighed against immediate and well-established bleeding risks.
“My biggest concern is that people may think that if they take aspirin today, they will be protected from cancer tomorrow,” says lead author Dr. Bo Jiang. “In reality, the potential protective effects take more than 10 years to manifest, if at all, but the risk of bleeding begins immediately.”
Not a one-size-fits-all approach
Previous research has shown that aspirin may help certain high-risk groups, such as people with genetic disorders such as Lynch syndrome, which increase the risk of colorectal cancer. However, this review focused only on individuals at average risk, for whom the long-term evidence was very uncertain.
The authors advise against starting aspirin for cancer prevention without first discussing your personal bleeding risk with your health care professional.
“This review highlights that we must move away from a one-size-fits-all approach,” said lead author Dr. Dan Cao. “The widespread use of aspirin in the general population is simply not supported by the evidence. The future lies in precision prevention using molecular markers and individual risk profiles to identify who will benefit most and who is most at risk.”
Overall, the researchers concluded that aspirin’s role in cancer prevention is more complex than previously thought. The balance of benefits and harms may change over time.
“As scientists, we have to derive evidence,” Dr. Zhang added. “Our rigorous analysis of the highest quality clinical trials reveals that the story of ‘aspirin for cancer prevention’ is more complex than a simple ‘yes or no’. Current evidence does not support blanket use of aspirin purely to prevent colorectal cancer.”
